An audible grunt, cough, or clearing of the throat issued by an individual while using a stall in a public men's restroom, especially when they hear someone else entering. This is done to advise the incoming patron that the stall is occupied, helping them avoid any awkward attempts to open the door or worse, peer through the crack in the door. A grunt is best because this bypasses any dialogue or conversation- both of which are widely regarded as taboo in a public men's room.

Cletus: so I was dropping a deuce at the mall when I heard the door open, so I gave an occupation grunt, right? But that fool didn't know any bathroom etiquette and tried to open my door anyway. As if my pants around my ankles behind the closed door wasn't enough of a giveaway!

DeSean: damn, son, I know what you mean. Same shit happened to me the other day when I was at White Castle. Thanks a lot, Obama.